This invention relates to ink jet or liquid drop recording, printing and the like systems. In particular, this invention relates to method and apparatus for generating continuous streams of liquid drops.
Liquid drop generators of the present type are described by Sweet in U.S. Pat. No. 3,596,275. Drops are generated continuously from a column of liquid emitted under pressure from a chamber via a nozzle. As characterized by Lord Rayleigh, drops continuously separate from the end of the liquid column in a predictable fashion. The uniformity of drop size and spacing are improved by stimulating the liquid at a fixed frequency. In addition, the stimulation stabilizes the location of drop separation from the liquid column. This is important for controlling the process of charging the drops by a charging electrode tunnel located at the drop separation region.
The problems associated with drop generation, such as non-uniformity in drop size and shape or in the non-stability of the drop break-off point, are most troublesome in multi-nozzle or multi-drop stream systems. Simply put, variations in drop parameters from nozzle to nozzle create control problems. The problems are especially difficult in systems where great accuracy in drop placement is required. An example of such a system is a high resolution ink jet printer.
Also, start up and shut down of an ink drop generator is troublesome in single as well as multi-nozzle drop generators. The liquid can cause electrical shorting and other problems if a liquid column and its drop stream are not appropriately handled at start up and shut off.